Trending At The PTAB: Collateral Estoppel Continues Evolving

Issue preclusion, or collateral estoppel, is a doctrine that prevents a party from relitigating an issue in a proceeding if that issue was actually litigated and necessary to the judgment in an earlier proceeding. Collateral estoppel typically applies to patent claims if the issues of patentability are identical — e.g., same claims, same prior art.¹

However, collateral estoppel is not limited to situations involving identical claims; instead, courts look at the underlying issues that were litigated and ultimately decided.

Estoppel generally, and collateral estoppel in particular, involving PTAB proceedings continues to evolve at the PTAB itself and across district courts.

As the Federal Circuit continues to weigh in on this area, we are starting to see brighter lines. Two recent cases addressing collateral estoppel illustrate this evolution. Both cases considered whether collateral estoppel should apply to factual findings on prior art from the PTAB in a later